Is your IR thermometer accurate? How do you know that your Infrared thermometer displays a correct reading?
My experience during going to a bank lead me to create this post. As part of the COVID-19 precautionary measures, before one can enter the bank, the guard will point at your face the IR thermometer gun to check your temperature. This is to detect if you have a fever (a temperature above 38 Deg C), if this is the case, they will not allow you to enter.
As we can see, monitoring instruments like the IR thermometer gun needs to be accurate in order to properly detect the temperature of a body that is being monitored. Any inaccuracy will result to a problem – “your health and safety depend on it therefore we need to have a proper verification procedure that is fast and simple to perform”.
This is where the importance of IR thermometer calibration comes in. And during calibration, we need to perform verification in order to detect any out of specifications.
In this post, I will share with you the following:
- What is an Ice bath?
- How to create a simple ice bath?
- What is an IR thermometer
- How to calibrate the Infrared thermometer using an ice bath?
- How to perform verification to determine the accuracy of IR thermometer
What is an Infrared (IR) Thermometer
An Infrared thermometer, also known as IR thermometer is a thermometer that is a non-contact type, which means it can measure a body’s temperature without making contact. It utilizes the radiated energy emitted by the body to detect and display as temperature.
What is the purpose of an IR thermometer?
We are using an IR thermometer, specifically the IR thermometer gun to measure temperatures that:
- Hard to reach areas
- Dangerous equipment like moving machinery
- Needs social distancing – for body temperature monitoring at a distance, just point and measure
- That needs faster response and results for immediate monitoring
Infrared thermometer works using the principle of the emissivity. The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation which is compared to a blackbody at the same temperature. A perfect blackbody has an emissivity of 1.
Read more about emissivity here >> emissivity
The default emissivity settings of most IR thermometer is 0.95.
When you are using an IR thermometer, the best results will be achieved if the emissivity of the object matches that of the IR thermometer settings. Some Infrared thermometers have an emissivity value that can be adjusted easily. Check this emissivity table for more emissivity value here >> emissivity table
In this post, I will present a calibration and verification in a zero point range using an ice bath with an emissivity of 0.97.
What is an ICE bath?
An ice bath is one of the oldest and simplest zero-point temperature source reference standards used in temperature calibration. It is a temperature comparator where we compare the reading of the UUC to an actual 0 ℃ fixed-point range. As the name implies, it is a simple combination of ice (shave or cube) and water that generates approximately 0.01 ℃ (0°C /32°F) temperature.
A properly prepared ice bath will give an accuracy or uncertainty of 0.002 ℃ (as per ASTM E563-11). This means that the lowest error (uncertainty) you can get when measuring an ice bath is 0.002 ℃ which is already negligible when using a simple thermometer with a resolution of 0.1℃.
Therefore, if you are measuring an instrument using an ice bath, you should read zero (0) (32°F) exactly.
For immediate calibration and verification, the ice bath is the best and easiest way to use as a reference standard. You can even prepare it even in your office for a quick verification setup.
Other important uses of an ICE Bath:
- For calibration of thermometers with thermocouple probes or RTD probes
- Calibration and verification of food thermometers
- Calibration of glass thermometers
- Used for cold-junction compensation for a thermocouple wire.
To know more about thermocouple and thermometer calibration, visit my other post here >> Temperature calibration
How to Make A Simple ICE BATH
Simple Steps On How To Create an Ice Bath.
Prepare enough water and ice cubes from purified (preferably distilled water) water. We are only aiming a result of approximately 0.0 ℃, so for this verification, it is not a problem to use regular purified water.
Step 1. Prepare the ice. If it is in big blocks, crush it to smaller sizes
Step 2. Prepare a container. A dewar flask is advisable but not required.
Step 3. Look for an ice shaver. Load the ice cubes to the ice shaver
Step 4. Shave enough amount where you can fill the container (dewar flask) at least ¾ or 75 percent.
Step 5. Wash the shaved ice with purified water to remove any contaminants and impurities.
Step 6. After washing, drain the water in the ice properly.
Step 7. Pour again the purified water until about 90% of the ice is soaked. See to it that the shaved ice will NOT float.
Step 8 Occasionally stir the mixture to avoid any lumps or spaces to form. Drain any excess water.
Step 9 Wait for around 2 minutes, then your ICE BATH is ready.
How to Perform Calibration of IR Thermometer Using the Ice Bath
1. Check the emissivity settings of the Infrared Thermometer gun, it should be within 0.95 to 0.97. A shave ice has an emissivity of 0.97.
2. Position the IR thermometer to the ICE bath where the distance of the tip and the ice is about 1 to 2 inches. This will ensure that the sensor’s field of view is inside the container.
3. Press the trigger button for 5 seconds to start measuring
4. Get the reading then record
5. Perform the procedure 3 times.
6. Get the average of the results then calculate the error.
How to calculate Error:
Error = UUC(Average) – STD
= 0.5 – 0.0
Error = 0.5 ℃
Note: This is considered as partial calibration (single point) used for verification at the lower range only. If you are using your IR thermometer for higher ranges (above 100 deg C) with strict tolerance, you need to send it to a qualified calibration lab.
How to Perform Verification to Determine the Accuracy of IR Thermometer
- If you already have a set tolerance, then skip steps 2 to 5
- Get the manufacturer’s manual of the IR thermometer.
- Refer to the specifications and get to the ‘Accuracy’ part. See the sample accuracy specs below.
- As per the above example, the accuracy at 0 ℃ = +/- 2.0. Now, this is also your tolerance limit
- The tolerance interval is 0+/-2 = -2 to 2
- Now, get the error from the result of the calibration above. Your reading should stay within these limits in order to be acceptable. See the below presentation to explain more.
- If it is outside this range, you need to perform an adjustment or send the thermometer to a qualified calibration lab for adjustment and full calibration.
I have seen a good example of ‘How to adjust an IR thermometer’ (this may apply to your IR thermometer). See the below video…
To know more about error and tolerance, visit this link>> Differences Between Accuracy, Error, Tolerance, and Uncertainty in a Calibration Results
The ice bath is the simplest and yet one of the most used reference standards for temperature calibration when properly prepared, it can provide an accuracy of 0.002 ℃. Enough to be used for an IR thermometer gun and other temperature instruments at a reference of ZERO Degree Celsius.
In this post, I have shared:
- What is an ICE bath?
- How to make a simple ice bath?
- What is an IR thermometer
- How to Calibrate the IR thermometer using an ice bath?
- How to perform verification to determine if the display of your IR thermometer is accurate.
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